Compound-arc, splined anchor

ABSTRACT

An intervertebral implant includes a body and a plate. The body has an upper surface defining an upper plane and a lower surface defining a lower plane. First and second fastener holes of the plate are configured to retain the heads of first and second fasteners. A portion of each of the shanks of the first and second fasteners extends from the first and second fastener holes beyond the upper plane. The shank portions of the first and second fasteners are curved in a direction away from the upper surface. The third fastener hole is configured to retain the head of the third fastener between the upper and lower planes. A portion of the shank of the third fastener extends from the third fastener hole beyond the lower plane. The shank portion of the third fastener is curved in a direction away from the lower surface.

RELATED APPLICATIONS

This application: is a divisional application of U.S. patent applicationSer. No. 15/001,502, filed Jan. 20, 2016; which is a divisionalapplication of U.S. patent application Ser. No. 13/937,208, filed Jul.8, 2013, issued as U.S. Pat. No. 9,248,029 on Feb. 2, 2016; which is acontinuation of PCT Application Serial No. PCT/US2012/020560, filed Jan.6, 2012; which claims the benefit of U.S. Provisional Patent ApplicationSer. No. 61/430,296, filed Jan. 6, 2011. All the foregoing referencesare hereby incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to implantable intervertebral implants andfasteners particularly useful for assisting with the surgicalarthrodesis (fusion) of two spinal vertebrae and more particularly, toan anchoring system that provides and controls limited movement betweenvertebrae during fusion.

2. Background Art

Various genetic or developmental disorders can affect the structure andfunction of the spinal column. Trauma or advancing age can lead tochanges in the bones, disks, joints, and ligaments of the spineproducing pain. Under certain circumstances, alleviation of pain can beprovided by performing a spinal arthrodesis, commonly known as a spinalfusion. This procedure is accepted and performed by the spinal communityand involves joining two or more adjacent vertebrae so that they are nolonger able to move relative to each other.

Many prosthetic devices are known for promoting fusion of the spinalvertebrae. The spine surgical community has accepted intervertebraldevices—commonly known as interbody spacers—as part of the state of theart and routine practice employs such devices for spinal arthrodesis.Surgeons insert these intervertebral devices to facilitate bone fusionin between and into the contiguous involved vertebrae. This fusioncreates a new solid bone mass, which acts to hold the spinal segment atan appropriate biomechanically restored height as well as to stop motionin a segment of the spine in which the patient is experiencing pain.Items surgically placed in these involved interbody regions can thusstimulate interbody bone in-growth such that the operated anteriorspinal segments heal into a contiguous bone mass; in other words, afusion occurs.

These prosthetic devices may be classified, in part, based upon theapproach to the spine through which they will be inserted (anterior,lateral, posterior, etc). They may also be classified based upon theirmechanism of spinal fixation (separate plate and screw fixation,incorporated blade/screw fixation, incorporated screw fixation withoutplate, blade fixation without plate). When referenced throughout thisdisclosure, the term “blade” can be considered to include a blade, anail, an anchor, and/or a non-threaded screw.

There are several commercially available devices that operate asstand-alone (that is, without support from an additional construct suchas an anterior plate and screws, or posteriorly placed screws and/orrods placed into the pedicles or facet joints) interbody fusion devices.These devices include the Stalif™, SynFix™, Zero-P™, and theVerteBridge™. The Stalif™ is a device for the fusion of the lumbarspine. The implant is inserted and fixed via diverging screws passingthrough pre-drilled apertures of the device that penetrate into thevertebral bodies without the use of a plate or locking of the screws.The screws are manually placed into the apertures of the device and aredriven using an appropriate tool, such as a surgical screw driver. TheSynFix™ is also a device for fusion of the lumbar spine that is placedin an intervertebral space and fixed via diverging screws passingthrough the device and into the vertebral bodies. Again, the screws aremanually placed into the apertures of the device and are driven using asurgical screw driver. The Zero-P™ is a cervical fusion device whichalso fixed via diverging screws passing through the device and into thevertebral bodies. Again, the screws are manually placed into theapertures of the device and are driven using a surgical screw driver.The VerteBridge™ is a device for the fusion of the cervical or lumbarspine in which anchoring blades are press-driven through apertures inthe device and into the respective vertebral bodies to fix the device inplace without the use of a plate.

All of the above-described devices have an anchor which is secondarilyadded to the initial device. The Stalif™, SynFix™, and Zero-P™ devicesemploy screws while the VerteBridge™ utilizes a blade anchor. Both theStalif™ and SynFix™ devices require the screws to be inserted attrajectories that are difficult to achieve given common human anatomicalstructures, especially at the spinal level L5-S1. Additionally, theproximal end of the screws may protrude anteriorly, causing potentialirritation to the great vessels overlying the lumbar spine. Due to theproblematic angulation of the screw trajectory, hinged screw drivers areprovided for their insertion. These difficult trajectories increase thedifficulty of insertion and increase the risk of injury to surroundingstructures. Rigid fixation through the SynFix™ or the Zero-P™ does notallow for the interbody graft to heal in compression which increases thechance of pseudoarthrosis (failure of fusion). The VerteBridge™ has apair of blades inserted after the initial device is put in place. Theseblades have a locking mechanism which cannot be released if removal ofthe implant is required. The locking mechanism is supposed to be ofsufficient strength to prevent failure and backout of the anchor toprevent irritation or injury to the great vessels overlying the lumbarspine or the esophagus overlying the cervical spine. Additionally, theblade anchors are supposed to exhibit sufficient biomechanics to allowappropriate segmental immobilization to promote solid arthrodesis. Inpractice, these features are not always achieved.

There are several commercially available devices that operate asanchoring devices placed in a direct lateral position in the lumbarspine. The XLP™, the ORACLE™, and the ZUMA™ employ a plate and screws tostabilize the anterior spine when an intervertebral device is placedthrough a direct lateral transpsoas approach to the lumbar spine. Thesefixation devices are placed over the lateral vertebral body and have thedisadvantage of risk to the traversing nerve roots which pass throughthis region. The ORACLE™ and ZUMA™ plating systems employ a four-holeplate for fixation and the width of the plate makes safe placementthrough this lateral region of the spine difficult. The XLP™ is atwo-hole plate that minimizes this risk but the plating system alsoencroaches on these traversing nerve roots. There currently is nostand-alone interbody fusion device that provides direct lateral lumbarfusion with biomechanical fixation while still protecting the nerveroots through this approach.

Further conventional devices are described by Donner/Synthes (April2009) wherein an Arcuate Fixation Member is described. Despite theaccurate description of a curvalinear anchor with multiple fixationpurposes, the described device is lacking in several areas as it relatesto interbody fusion. First and foremost, the broad description of thearcuate anchor lacks critical specifications. Relative to interbodyfusions, regardless of whether the anchor is curvalinear in a continuousor noncontiguous fashion, the final angulation relative to thehorizontal plane may be critical. If the resulting angulation is notwithin 50-90 of the horizontal plane, the device cannot be expected toimprove that currently available. Further, the mating boring guide willloosen the anchor and its fixation from the outset, and the taperedshaft will decrease bone surface area contact and fixation. The devicealso lacks guiding splines on the blades with a matching portal throughthe fixation plate for reproducible accurate blade placement. Absentalso is a top loading introducer for matching the portal through theplate to overcome the current difficulty with screw trajectory. This isperhaps the most important aspect as patient safety is at risk with theuse of hinged screwdrivers, drills, and awls. Thus, the arcuate fixationmember will fail to overcome the problems inherent with the currentdevices available.

It may be desirable to provide an intervertebral device for the fusionof the cervical or lumbar spine in which anchoring blades are placedthrough apertures in the device and into the respective vertebral bodiesto fix the device in place with the use of a plate. This device wouldutilize helical or non-helical angled blades which are locked to aplating system to prevent back-out and risk to the great vesselsoverlying the lumbar spine, and prevent risk to the esophagus overlyingthe cervical spine. This plate would also avoid risk to the traversingnerve roots through the direct lateral or transpsoas approach to thelumbar spine. This anchoring system may have the benefit of functioningas a stand-alone intervertebral device or as a separate plating deviceby itself. This intervertebral device would allow for safe removal ifnecessary. This device would also overcome the problems encountered withthe current art requiring screws to be inserted at trajectories that aredifficult to achieve given common human anatomical structures and wouldnot require insertion with screw drivers or hinged screw drivers. Thisdevice would also allow fusion segments to heal in compression, allowingfor increased fusion rates as a result of the blade design.

It may be desire to provide an intervertebral device that would utilizeangled blades with either linear or helical spines. The curvalinearradius of the splined blade anchor may result in a terminal angulationof 50-90 degrees as measured from the horizontal plane. This feature isdisregarded in the prior art ignoring Wolfs law which states that boneheals best in compression. It may be further desirable to provide adevice without a slidabably mating curved guiding bore through which thecurved anchor is inserted, as this may cause the curved bone anchor tobe inserted loosely. There will instead be no need for this as theconfiguration of the splined blade and its mated portal through thefixation plate will guide the anchor to its ideal position withoutcompromising tight fixation.

It may be desirable to provide a device with a minimum of two fixationblades, and in some aspect preferably three. This may afford moreadequate biomechanical fixation and allow use at multiple consecutivevertebral levels as well as levels above or below previouslyinstrumented vertebral segments. Superior and inferior Blades will beoriented in a directly opposing manner as referenced from the horizontalplane optimizing compressive subsidence of vertebral segments.

It may be desirable to provide a device with a minimum of two splinesorientated in either a linear or helical fashion with respect to thelongitudinal axis of the blade whose purpose is to guide the bladeaccurately to its correct position within the bone. There may be notaper between the proximal and distal ends allowing for largercontiguous surface area for bone fixation. The head or proximal end ofthe blade may have the same spline orientation as the shaft so therewill be no change in course throughout the entire length of the bladesinsertion through bone. The proximal end and head may not only have samespline orientation but may also have a morse taper matching the guidingchamber of the plate. The proximal end, head, with the features above,may seat into the plate such that the spines would be below the anteriorsurface of the plate allowing for a single cover screw to preventbackout if the morse taper was felt to be inadequate.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention are stand-alone interbody devices,which may be designed in the general style of an anterior lumbarinterbody fusion (ALIF) device, a transforaminal lumbar interbody fusion(TLIF) device, a posterior lumbar interbody fusion (PLIF) device, anextreme lateral or direct lateral interbody device fusion device, or ananterior cervical interbody fusion device.

The device includes a body made from any variety of structuralbiomaterial including, but not limited to, polyetheretherketone (PEEK),Titanium, carbon fiber, ceramic, etc. The body may have serratedsuperior and/or inferior surfaces to provide initial resistance againstmigration. Additionally, there may be at least one opening extendingfrom the superior surface to the inferior surface for the purpose ofcontaining osteo-inductive, osteo-conductive material, such asautograft, bone morphogenetic protein (BMP), or one of a variety of bonegraft substitutes as is the accepted practice in the spinal community.

According to various aspects of the disclosure, an intervertebralimplant may include the above mentioned body and a plate associated withthe body. The plate may be mated with the body prior to insertion or maybe modular in that it may be attached after the body is inserted intothe intervertebral space. The plate may be implanted independently fromthe body of the device. The plate may be inserted to fit inside theinterbody space completely or level with the anterior surface of thevertebral body so as not to interfere with the great vessels lying overthe lumbar spine or the esophagus anterior to the cervical spine. Theplate may be inserted to fit inside the interbody space completely orlevel with the lateral surface of the vertebral body so as not tointerfere with the nerve roots when inserted through a direct laterallumbar approach.

The plate includes at least a superior and inferior fastener hole.Additional fastener holes may be included dependent on the spinalsegment being addressed for fusion. At least a third fastener hole isenvisioned when utilized within the anterior lumbar spine forbiomechanical stability.

The implant includes at least superior and inferior fasteners eachhaving a head and a shank. The first and second fastener holes may beconfigured to retain the heads of the first and second fastenersrespectively between the upper and lower planes. A portion of each ofthe shanks of the first and second fasteners extends from the first andsecond fastener holes respectively beyond the upper plane.

The shank portions of the first and second fasteners may be curved in adirection away from the upper surface of the body. This angular featureallows for insertion of the fastener through a unique top loadingapproach through the plate. This unique feature overcomes the problemsencountered with the current art requiring screws to be inserted attrajectories that are difficult to achieve given common human anatomicalstructures and would not require insertion with screw drivers or hingedscrew drivers.

The third fastener hole may be configured to retain the head of thethird fastener between the upper and lower planes. A portion of theshank of the third fastener extends from the third fastener hole beyondthe upper plane. The shank portion of the third fastener may be curvedin a direction away from the upper surface of the body.

In accordance with some aspects of the disclosure, a fastener for anintervertebral implant may include a head portion and a shank portionextending from the head portion. The shank portion may have asubstantially circular cross section adjacent the head portion and aflattened free end opposite the head portion. The shank portiontransitions from the circular cross section to the flattened free end ina substantially continuous manner. At least one spine may be arrangedhelically on the shank portion. The spine may extend from the circularcross section to the flattened free end.

One of the benefits of the embodiments of the invention is the ease withwhich the device may be used. There are fewer steps as compared withconventional devices because there are no screws to be inserted and thespiral blades can be inserted, through the same device used forinsertion of the plate, in a top loading fashion. Furthermore, becausethe spiral blades are angled relative to the intervertebral plane, thereis no difficult trajectory needed to place the screws as with previousdevices. As opposed to devices employing blades without plate fixation,the embodiments of the invention employ spiral blades affixed to a rigidplate, which provide better fixation, stabilization, and the ability toremove this device without destruction of the vertebral anatomy ifrequired.

Some further advantages and embodiments may become evident from theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in:

FIG. 1 is a top perspective view of an exemplary intervertebral implantin accordance with various aspects of the disclosure.

FIG. 2 is a front perspective view of an exemplary intervertebralimplant in accordance with various aspects of the disclosure.

FIG. 3 is a top perspective view of an exemplary fastener in accordancewith various aspects of the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate an exemplary intervertebral implant 100 inaccordance with the disclosure. An intervertebral implant 100 generallyincludes a body (or housing) that is sized and shaped to fit in theintervertebral space between adjacent vertebral bones (not shown) of thehuman spine. It is understood that the size and shape of the device 100may be adapted to fit in an intervertebral space at any level of thespine, such as the cervical spine, thoracic spine, or lumbar spine. Theintervertebral device 100 as illustrated in this example is designed tobe a stand-alone device, having a plate 130 attached through a locked ormodular attachment (e.g., requiring no separate anchoring devices),which is inserted into the inter-vertebral space from an anteriordirection. This embodiment is in the general form of an ALIF device,although as will be appreciated from the description herein, the devicemay be adapted to operate as an extreme lateral or direct lateralinterbody device, an anterior cervical interbody device, or a TLIF orPLIF device.

The body 110 has an upper surface 112 defining an upper plane and alower surface 114 defining a lower plane. The body 110 also includes ahorizontal center plane intermediate the upper and lower surfaces 112,114 and substantially parallel to the upper and lower planes defining alongitudinal axis. With reference to FIGS. 1 and 2, it is understoodthat the longitudinal axis may not be precisely normal to the first andsecond major surfaces 112, 114 as there may be a slight narrowing height(taper) to the body from the anterior sidewall 116 to the posteriorsidewall 118. This taper is designed to accommodate the natural anatomicrelationships between the adjacent vertebral bones, thereby maintainingthe normal lordodic curvature of the spine.

The body 110 may include a plurality of cutouts 122, 124, 126 extendingthrough the body 110 from the upper surface 112 to the lower surface114. These cutouts are used to provide the trajectory of the fasteners.According to various aspects, the body 110 may be comprised ofpolyetheretherketone (PEEK) or other radiolucent material, such as acarbon fiber composite, which is well suited for fabrication of thebody.

According to various aspects, the upper and lower surfaces may bedesigned to rest against the end plates of two adjacent vertebrae and/oragainst upper or lower surfaces of another implant 100. To achieveimproved anchoring, the upper and lower surfaces 112, 114 may betopographically shaped and/or may be fitted with gripping members 116,such as for example, serrations, grooves, ribs, or teeth, or theirsurfaces may be roughened in any known manner. In some aspects, the body110 may include one or more sidewalls 117. The sidewalls 117 may includegripping members 120 (e.g., serrated wall) to facilitate improvedanchoring.

The implant further includes a plate 130 that is matable with the body110. Titanium is suitable material for the plate 130. As shown in FIGS.1 and 2 the plate 130 is mated with the anterior face 116 of the body.However, other embodiments of the fusion implant are configured formating the plate 130 to the body 110 at locations other than theanterior face 116 as required for the direct lateral approach to thespine.

The plate 130 includes an upper surface 132 lying substantially in theupper plane of the upper surface 112 of the body 110 and a lower surface134 lying substantially in the lower plane of the lower surface 114 ofthe body 110. The plate 130 includes a first surface 136 extendingsubstantially perpendicular to the upper and lower surfaces 132, 134 andupper and lower planes, and facing the body 110. It should beappreciated that the upper and lower surfaces 132, 134 of the plate 130may include gripping members (not shown), such as serrations, grooves,ribs, or teeth, or their surfaces may be roughened in any known mannerto facilitate improved anchoring.

Although the plate 130 can be bonded to the body 100 so that the plateand body cannot move with respect to each other via a rigid rivetmechanism, they can also be mated through a modular mechanism allowingthe plate 130 to be attached to the body 100 before or after the bodyhas been inserted into the interbody space. For example, in theillustrated embodiment, the plate 130 is bonded through a rivetattachment to the body 100. However, it is envisioned that an additionaloption would be for the plate 130 to be attached to the body 100 througha threaded screw attachment, a cam and shaft attachment, or a rotationallocking tab.

It should be appreciated that in other embodiments, the plate 130 may beembedded in the body 100. For example, an embedded portion (not shown)of the plate 130 may extend from the first surface 136 and be receivedby the body 100. In some aspects, the body 100 may then be mouldeddirectly to the plate 130 via the embedded portion. In other aspects,the plate 130 may be embedded in the body 100 in any conventionalmanner.

The plate 130 includes a second surface 138 extending substantiallyperpendicular to the upper and lower surfaces 132, 134 and upper andlower planes, and facing in a direction opposite to that of the firstsurface 136 away from the body 110, for example, in an anteriordirection upon implantation of the implant 100 intervertebrally.

The plate 130 includes one or more boreholes configured to receive afastener. Although the illustrated embodiment shows three boreholes, itshould be appreciated that other embodiments may include two boreholesor more than three boreholes. As shown in FIGS. 1 and 2, in one aspectof the disclosure, the boreholes include a first fastener hole 142, asecond fastener hole 144, and a third fastener hole 146. The first,second, and third fastener holes 142, 144, 146 each have an axis angledfrom about 25 degrees to about 70 degrees with respect to the horizontalcenter plane of the implant body 110. In some aspects, the axes of thefirst, second, and third fastener holes 142, 144, 146 are angled fromabout 35 degrees to about 50 degrees with respect to the horizontalcenter plane.

The implant 100 may include a plurality of fasteners 150, 150′, and 150″such as, for example, blades. Each fastener 150, 150′, 150″ may includea head portion 152 and a shank portion 154. The shank portion 154extends from the head portion 152. The shank portion 154 has a region(not shown) adjacent the head portion 152 with a substantially circularcross section. The shank portion 154 includes a flattened free end 158opposite the head portion 152. According to various aspects, the shankportion 154 transitions from the circular cross section region to theflattened free end 158 in a substantially continuous manner. In someaspects, the shank portion 154 curves along its length, as shown inFIGS. 1 and 2.

Referring to FIG. 3 each fastener 150 may include one or more splines160 arranged helically on the shank portion 154 that facilitateself-tapping into a vertebra. In some aspects, one or more of thefasteners 150 may include two or more splines 160 that commence atdifferent sides, for example, in some aspects diametrically oppositesides, of the circular cross section region 156 of the shank portion 154and spiraling helically at substantially the same pitch along the lengthof the shank portion 154 and terminate at opposed sides of the free end158. In some aspects, the splines 160 wrap around about one quarter of aperiphery of the shank portion 154 as the splines 160 extend along thelength of the shank portion 154. In some aspects, the splines 160 mayextend in a non-spiraling manner along the axis of the shaft.

According to various aspects, the head portion 152 of at least one ofthe fasteners 150 conically tapers toward the shank portion 154. Atleast one of the first, second, and third fastener holes 142, 144, 146has a conical surface (not shown) so as to complement the conical taperof the fasteners. As the fastener hole 142, 144, 146 tapers conicallytowards its underside, a fastener 150 fitted with a matching conicalhead may be rigidly anchored in said borehole. In some aspects, theconical fastener hole exhibits a cone angle smaller than the resultantangle of friction. For example, the fastener hole's conicity may be1:3.75 to 1:20, and in some aspects from 1:5 to 1:15.

Referring again to FIGS. 1 and 2, the first and second fastener holes142, 144 may be configured to retain the head portion 152 of the firstand second fasteners 150′, respectively, between the upper and lowerplanes defined by the upper and lower surfaces 112, 114 of the body 110.A portion 154 of the shank of the first and second fasteners 150′extends from the first and second fastener holes 142, 144 beyond theupper plane. In some aspects, the shank portion 154 of the first andsecond fasteners may be curved in a direction away from the uppersurface 112 of the body 110. The third fastener hole 146 may beconfigured to retain the head portion 152 of the third fastener 150″between the upper and lower planes defined by the upper and lowersurfaces 112, 114 of the body 110. A portion 154 of the shank extendsfrom the third fastener hole 146 beyond the lower plane. The shankportion 154 may be curved in direction away from the lower surface 114of the body 110. This curved angulation of the shanks relative to theupper and lower surfaces 112, 114 allows for top loading of the spiralblade anchors into their relative vertebral segments into which they areplaced for fixation.

The spiral blade fasteners are coupled to the plate through the matedtapered heads. Alternatively, they are locked to the plate via a coverplate or an expanding head, or a locking cap, or a locking tab, or alocking seal, or a locking ring, or a locking lip.

According to some aspects of the disclosure, the upper surface 112 ofthe body 110 may be at least partially configured to lie adjacent to theendplate of a first vertebra, and the lower surface 114 of the body 110may be at least partially configured to lie adjacent to the endplate ofa second vertebra. In some aspects of the disclosure, the upper surface112 of the body 110 may be at least partially configured to lie adjacentthe lower surface of another intervertebral implant similar in structureto the implant 100 presently described, while the lower surface 114 ofthe body 110 may be at least partially configured to lie adjacent to theendplate of a second vertebra. In some aspects of the disclosure, theupper surface 112 of the body 110 may be at least partially configuredto lie adjacent to the endplate of a first vertebra, while the lowersurface 114 of the body 110 may be at least partially configured to lieadjacent the upper surface of another intervertebral implant similar instructure to the implant 100 presently described.

It should be appreciated by persons skilled in the art that the size ofthe body 100, plate 130, and fasteners 150, 150′, 150″ may be varied tofacilitate implantation at different regions of the spinal column. Forexample, the length and/or width of the body 100, plate 130, andfasteners 150, 150′, 150″ may be made smaller for use in the cervicalregion as compared with the thoracic and lumbar regions. On the otherhand, the length and/or width of the body 100, plate 130, and fasteners150, 150′, 150″ may be made larger for use in the lumbar region ascompared with the thoracic and cervical regions.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the intervertebral implantsof the present disclosure without departing from the scope of theinvention. Throughout the disclosure, use of the terms “a,” “an,” and“the” may include one or more of the elements to which they refer. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only.

What is claimed and desired to be secured by United States LettersPatent is:
 1. An anchor comprising: a head defining a centerlinetherethrough, the head having an outer end and a shank end opposite oneanother along the centerline; a shank formed to extend from the headtoward a point end, defining therebetween a central axis of the shankand a cross section, the central axis curving in a first helicaldirection away from the head along the central axis; splines extendingfrom the shank, each spline extending along the shank and extendingradially away therefrom; and a point, at the point end of the shank,comprising an edge sized and shaped to penetrate bone.
 2. The anchor ofclaim 1, wherein: the shank and splines are together sized and shaped toresist withdrawal in response to a force on the head in a direction awayfrom the shank along the centerline.
 3. The anchor of claim 2, whereinthe shank has a length, a circumference therearound defining a diametercorresponding thereto, and an aspect ratio of the length to thediameter; the aspect ratio is greater than three; the first helical pathresults in the shank having a pitch (distance per one full revolution)greater than the length.
 4. The anchor of claim 3, wherein the pitch ismultiple times the length.
 5. The anchor of claim 3, wherein the splinescurve along a second helical path distinct from the first helical pathwith respect to the central axis.
 6. The anchor of claim 5, wherein: theanchor is shaped to maintain the object against the bone in compressionfollowing installation of the anchor; and the compression is supportedby resistance of the splines to motion along the centerline byresistance of the splines to movement in a direction other than at leastone of the first helical path and the second helical path.
 7. The anchorof claim 1, further comprising: a second head and a second shankconfigured as the first head and shank.
 8. The anchor of claim 7,further comprising: a frame having a first side, a second side, andprovided with apertures sized and shaped to receive and direct the firstshank and second shank into bone on opposites ones of the first andsecond sides, wherein the first and second shanks are formed of a firstmaterial and the frame is comprised of a second material selected frommetal or plastic, wherein the frame comprises a horizontal center plane,and wherein each of the apertures provided has an axis angled from about25 degrees to about 70 degrees with respect to the horizontal centerplane.
 9. The anchor of claim 1 wherein the object is not bone material.10. An anchor comprising: a head defining a centerline therethrough froman outer face to a shank; the shank, having a central axis defining across section and a first helical angular direction orthogonal to thecross section, the central axis being non-linear in shape and curvingalong through the center of the cross section from the head along thecentral axis; splines extending from the shank, each spline extendingradially away from the first helical direction; a point, extending fromthe shank opposite the head, the point comprising an edge sized andshaped to penetrate bone; the shank and splines, each sized and shapedto resist withdrawal in response to a force on the head in substantiallyevery translational direction alone and every rotational direction alonewith respect to the centerline; the shank and splines defining a lengththereof, a circumference therearound, a diameter corresponding to thecircumference, and an aspect ratio of the length to the diameter greaterthan three, wherein the first helical angular direction has a pitch(length per full revolution about the central axis) greater than thelength and the head, shank, and splines are formed of a singlehomogeneous material.